This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
Blind equalization is a digital signal processing technique of using signal statistics of a received signal to infer (equalize) the transmitted signal from the received signal, while making use of the transmitted signal statistics.
Blind equalization may be viewed as essentially blind de-convolution applied to digital communications. Nonetheless, the emphasis in blind equalization is on online estimation of the equalizer filter (which is the inverse of the channel impulse response) rather than estimation of the channel impulse response itself. This is due in part to the common use of blind equalization in digital communications systems as a way to extract the continuously transmitted signal from the received signal.
One modulation format is polarization-switched (PS) Quadrature Phase-Shift Keying (QPSK). Various approaches to blind equalization in PS-QPSK have been investigated, but suffer from various impairments that render PS-QPSK an unsuitable modulation format for some applications, such as long-haul optical fiber communications.